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L0301P84 - Introduction to Microbes
Domains of the Living World *based on molecular evidence (rRNA) *all organisms divided into 3 domains **bacteria (prokaryotes) **archaea (prokaryotes that are able to live under extreme conditions) **eukarya (eukaryotes) Microorganism *too small to be seen without magnification i.e. light or electron microscope *cell diameters range between ~1-100μm *includes: **all prokaryotes (bacteria and archeans) **single celled eukaryotes - some fungi, most protistans, some plants **viruses Prokaryotes and Eukaryotes *chemically similar *both surrounded by a plasma membrane *structurally very different within the cell *prokaryotic cells are smaller and have a greater surface area to volume ratio Prokaryotes *almost all are unicellular *lack nuclei and membrane-bound organelles **contain genetic, protein synthesis systems *are different shapes depending on their type of cell wall **coccus (spherical) - Enterococcus sp. **bacilli (rod shaped) - Escherichia coli **spiral (long curly) - Leptospira interrogans Common Features *nucleiod = genetic material ≠ nucleus *specialised features for function: **cell wall **double membrane (inner and outer) **capsule Prokaryotic Cell Wall *common target for combating disease *antibiotics specifically interfere with synthesis of peptidoglycan and thus little or no effect on cells of humans Unique compounds in bacterial cell walls: *peptidoglycan **unique to bacteria **complex carbohydrate **forms a strong mesh around the cel **80% in gram +ve, 10-20% in gram -ve *lipopolysaccharide (LPS) **lipid sugar molecule **embedded in the outer membrane **mimic glycoprotein/lipids on self cells **inflammatory molecule ***cause toxic shock when released from the bacteria *D-amino acids **very rare but are believed to help bacteria adapt to new environments Gram Staining *Hans Christian Gram - 1884 *separates most bacteria into two groups **i.e Gram positive or negative Procedure *smear of cells *stain with crystal violet *treat with iodine *wash in alcohol **more peptidoglycan = more stain retained *counterstain with safranin (red) Prokaryotic External Structures Flagella *allow for motility by rotating like a propeller *long filament - made of protein flagellin *bacteria can have **one or multiple flagella **on one end, both ends or all over Pili and Fimbriae *project from the surface of bacteria *shorter than flagella - threadlike *aid in adherence of bacteria to surfaces within the host and on inanimate objects *sex pilus allows for DNA transfer Prokaryotic Cell Replication Binary Fission *simple and fast **replicate genome, extend cell wall and membrane, and then divide Prokaryotic Environments *found ubiquitously (everywhere) **hot, cold, acidic, alkaline, salty **aerobic (with oxygen) **anaerobic (without oxygen) *oxygen requirements **strict aerobes - will die without O2 **microaerophilic - prefer low oxygen levels **facultative anaerobes - with or without O2 **aerotolerant anaerobe - will not die in O2 **strict anaerobes - will die in O2 **other - e.g. carbon dioxide Medically Important Bacteria *Listeria monocytogenes **listeriosis *Carrpylobacter jejuni **gastroenteritis *Mycobacterium tuberculosis **tuberculosis *Staphylococcus aureus **skin infections; pneumonia; endocarditis; toxic shock syndrome (TSS); meningitis; osteomyelitis; septicaemia *Escherichia coli **food borne outbreaks leading to kidney failure (haemolytic uremic syndrome) *Legionella pneumophila **Legionnaires' pneumonia *Helicobacter pylori **gastric and duodenal ulcers *Clostridium difficile **opportunistic pathogen - antibiotic induced diarrhoea; colon damage *Streptococcus pyogenes **skin infections; pharyngitis (strep throat); necrotizing fasciitis (GAS); TSS *Pseudomonas aeruginosa **opportunistic pathogen - urinary tract, respiratory system, soft tissue, bone and joint, gastrointestinal infections **particularly affects cystic fibrosis patients Eukaryotes *animals, plants, fungi, protists *have membrane bound organelles = more complex intracellular processes Medically Important Eukaryotes Protists *Plasmodium sp. - malaria *Trypanosoma sp. - african sleeping sickness *Entamoeba sp. - amoebic dysentery Fungi *Candida albicans **oral and genital infections (thrush) *Dermatophytes - ringworm; tinea *Aspergillus **aspergillosis: infections of the lung, inner ear, sinuses, eye (rare) Prokaryotes vs Eukaryotes Viruses not classified in three domain system very small visualised by electron microscope 0.1 μm3 (poxvirus) 0.0005 μm3 (influenza virus) 0.00001 μm3 (poliovirus) not comprised of cells - acellular obligate intracellular parasites use machinery of host cells to multiply develop and reproduce only within specific hosts can affect animals, plants, fungi, protists and prokaryotes Virion (Single Virus) virus genome nucleic acid - DNA or RNA surrounded by a capsid or protein coat comprised of one or more repeating protein subunits may have an envelope a lipid and protein membrane acquired from the host cell (animal viruses) Classification of Viruses type of nucleic acid DNA or RNA never together morphology shape, size, symmetry of capsid envelope presence or absence host and host range narrow or broad disease produced Virion Shapes Helical Viruses look like matchsticks genome packaged within a tube of protein subunits Icosahedral Viruses genome in the centre of the icosahedron can be a “naked” or enveloped virus Medically Important Viruses DNA Hepatitis B virus hepatitis-inflammation of the liver Herpes simplex virus oral and/or genital herpes Papillomavirus skin warts; genital HPV infection RNA Influenza - flu Paramyxovirus - measles Rotaviruses - diarrhoea and gastroenteritis Retroviruses Human Immunodeficiency virus (HIV) Acquired immunodeficiency syndrome (AIDS) Beneficial Microorganisms Normal Microbiota humans have normal flora found on epithelial surfaces except the lower respiratory tract and upper urinary tract are highly beneficial